The invention relates to measurement of speed and acceleration of fluids, in particular with regard to ultrasound technology.
The speed of sound in air along a line or path between any two points may be determined by measuring the time taken for the sound to travel between the two points. With the air moving from one point to the other, sound traveling in the same direction is speeded up, while sound traveling in the other direction is slowed down. Where the actual wind has a speed W in a direction which is at an angle xcex8 to the sound speed line, then the wind component along that line is W cos xcex8, and the wind component along a line that is perpendicular to the sound speed line is W sin xcex8. In such a case, the sound speed S along the line is So+W cos xcex8, where So is the sound speed in still air. If the distance over which the sound speed is being measured is D, then the time T taken is D/S. Thus, T=D/(So+W cos xcex8).
Heard U.S. Pat. No. 4,336,606 (xe2x80x9cHeard) discloses methods and apparatus for detecting and measuring a wind gradient at a location by comparing the wind speed in the same direction at two or more heights at the location. The comparison based upon a comparison of the speed of sound in a direction and at specific heights, a difference in the apparent speeds indicating the presence of wind gradient. The disclosure involves: beaming a regular sound wave train between a transmitter/receiver pair positioned and like orientated at each of two or more heights at the location; noting each transceiver pair""s received sound wave train phase, and comparing it with its transmitted phase, so as to deduce the wind-caused phase change; and using these deduced phase changes to calculate the actual wind speeds, and thus the relative changes of wind speed with height, in the selected direction. Heard""s apparatus, however, has the transmitter/receiver pairs positioned at too great a distance (approximately 200 feet) for the measurement to be effective and accurate. In addition, applying the teachings to an airplane landing situation is not practical as the noise level of an incoming plane is too large and will interfere with the accurate and timely measurements of the ultrasound transmissions.
Gill U.S. Pat. No. 5,163,331 (xe2x80x9cGillxe2x80x9d) discloses a fluid speed measurement device that includes a pair of ultrasonic transducers spaced in a measuring chamber. A transmitter and receiver system is controlled by a microprocessor which generates pulses which periodically invert and these are switched by switches that allow alternate direction of transmission. Reception and detection of signals is effected by particular blocks. Time calculation is determined by a counter and results are used to calculate flow speed or volume using a microprocessor. A speed increase in the measurement region is effected using a venturi device. The device disclosed in Gill, however, is a closed device. In a closed configuration, the speed of a gas is higher than the speed of the same gas in an open configuration. The disclosed system therefore is not required to be sufficiently sensitive to detect signals in such a fluid wherein the speed is not so high, as in, for example, the atmosphere.
Herrmann et al. U.S. Pat. No. 5,804,739 (xe2x80x9cHerrmannxe2x80x9d) discloses a xe2x80x9cmethod of determining the time point (t0) of the start of a high frequency oscillation packet triggered as a result of a corresponding external excitation which is extremely tolerant relative to systematic disturbances from various sources that consists of determining the times at at least two points of the envelope curve of the oscillation packet with respect to an arbitrary zero time point. Of these two points one is a characteristic point of the envelope curve and the other has an amplitude equal to a predetermined fraction of the amplitude at the characteristic envelope curve point. It is preferable that during xe2x80x9c. . . calculation the angle between the directions of the ultrasonic pulse packets and the flow direction of the medium, . . . differs significantly from 90 degree, is particularly taken into account.xe2x80x9d Hermann does not, however, disclose nor suggest automatic calibration for pressure-temperature, nor portability, no that the size of the measuring device be of a relative small size.
It would be advantageous to provide a fluid speed measurement apparatus along with a process that takes digital measurements.
It would be advantageous to provide a fluid speed measurement apparatus along with a process that uses a protective, ventilated material, such as, for example, a lightweight plastic, to allow for automatic calibration to pressure-temperature.
It would be advantageous to provide a fluid speed measurement apparatus along with a process that is small enough and portable to be used at an airplane runway for measuring wind velocity and direction, yet placed far enough away from the runway so that loud airplane noises cannot interfere with the measurement apparatus and process.
It would be advantageous to provide a fluid speed measurement apparatus along with a process that has no moving parts, such as, for example, a ventilator or moving flap used in detecting fluid speed.
Methods and apparatus for using ultrasound technology to measure speed and acceleration in fluids are provided. Three exemplary embodiments are disclosed. The first exemplary embodiment measures fluid velocity, such as, for example, wind, under standard atmospheric pressure-temperature. The second exemplary embodiment measures fluid velocity, such as, for example, wind, affected by and automatically calibrates for pressure and temperature. The third exemplary embodiment measures gas or air density, such as, for example, density altitude. Applications of the invention include wind direction and speed calculation in agriculture, aviation, hydraulics, and other industries.